Short wave antenna system



0a. 24, 1939. A, ALFQRD N 2,177,416

SHORT WAVE ANTENNA SYSTEM Filed March 15, 1958 IL am L- vill FIG. 1.

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INVENTOR ANDREW 4L FORD BY ATTORNEY Patented Oct. 24, 1939 2,177,416?

UNITED S ATES rArENr OFFIQE SHORT WAVE ANTENNA SYSTEM Andrew Alford, San Mateo, Calif., assignor to Mackay Radio & Telegraph Company, New York, N. Y., a corporation of Delaware Application March 15, 1938,.SerialNo. 195,946

4 Claims. (Cl. 25033) The present invention relates to antenna 'systhese long waves. In such cases the efiiciency tems, and especially to short wave antenna sysof the radiating or collecting system is greatly tems of the tuned antenna type. The invention reduced by the low radiation resistance of such is particularly applicable to systems for use with a short antenna. It has therefore come to be 5 .short wavelengths, for example, Wavelengths in -g n r lly ccep e rul tha an antenna Whose .5 the range of from 5 meters to 60 meters. length is only a small fraction of a wavelength It is an object of the present invention to promust inherently result in a low efiiciency of radivide an antenna system of unusually compact ation or collection of energy.

, form and small dimension. More particularly, it I In accordance with my invention, however, in m isan object to provide an unusually compact dishort wave systems the antennae m y be short- .1 I rective'antenna system of the dipole type, which, ened to a very small fraction of a wavelength shall be small enough to render it convenient to without a corresponding decrease in o le in r rotate the complete-antenna with approximately a fil n Y- the. same convenience-as a loop antenna. A careful analysis of the factors which cause It is'a further object of my invention to mm the reduction of efiiciency when the radiation 1 vide an antenna system of simple design which resistance of an antenna is reduced, indicates is readily adjustable for use at a number of difthat this reduction of eificiency results from the ferent frequency ranges, and especially to profact that the radiation resistance of the anvide such anantenna system in which the necestenna becomes 'comparable with or smaller than '20 sary adjustments in changing from one 'frethe effective resistance-resulting from other facg .quency t another in t Same al range or tors, such as heat losses in the antenna itself, i changing from one frequency range to anand especially power losses resulting from circuother frequencyrange, can be effected in a parlatory currents-in the tuned system immediately ticularly convenient manner. associated with theantenna. It is .a particular object of my inventio t In accordance with my invention, therefore, a 25 provide a compact, readily adjustable antenna veryismalldipole antenna is immediately assosystem whose overall efliciency is substantially .ciated with a tuned circuit constituted wholly or as high as that of a larger antenna system. p in ipa ly y a e h r' wire s s m, r r n v accordance ith my invention, compactmissionline type of resonant circuit, which has ness is attained in a short wave antenna Witha very low loss. The use of such a very low l ss 30 out-any substantial sacrifice of efiiciency. circuitimmeoliately associated with the antenna .In accordance with a further feature of my does not in itself produce a substantial increase invention, the antenna system is rendered opin efficiency with antennae of normal dimension, erative for arelatively wide range of frequenbut the use of such a low loss circuit does very cies by providinganadjustabletuning circuit of greatly reduce the minimum dimensional limit 35 the transmission line type, while at the same. below which the antenna length cannot be retime convenience in effectingsmall frequency adduced without substantial reduction of efficiency. justments of'the antenna isattained by further By the use of a v r l w loss res n n e ir uit providing a'trimmer condenser connected in of the transmission line type immediately as- =shuntwith the antenna. The resonant transsociated with a radiating or receiving antenna, 40 mission line 'which is used to tune the antenna I have found that the overall antenna length in "accordance with my invention not only procan .be .reduced to a very small fraction of a vides the above mentioned advantage of renwavelength, for example, to one-tenth of a wavedering the antenna semi-universal in respect length or less, without any substantial reduction to its frequency range, but also provides a very of efficiency. 45 low loss resonant "circuit immediately 'associ- The exact nature of my invention. can best be ated withthe antenna, so that the reduction of understood by reference to the .attached drawantenna dimensionsmaybe carried beyond the in in which usual limit without-substantial reduction of over- Fig. 1 represents a portabl receiving s s em .50 r all efiiciency. in accordance withmy invention, and a .Although antennae Whichare only a small Fig. 2 represents a portable directional refractionof a Wavelength long have been used 'ceiving system in accordance with my invention. A for reception'of long waves, such dimensions have Referring more particularly to Fig.1, I and 2 only "been employed because of the prohibitive are a pair of conductors disposed on a common cost otproviding antennae of adequate length for axis so as to constitute a dipole. An open-wire transmission line 3 provided with an adjustable short circuiting bar 4, is directly connected to the conductors I and 2, and serves as a loading impedance for tuning the dipole antenna to resonance. The length L of each of the dipole conductors l and 2 is a very small fraction of a wavelength, preferably between one-fifteenth and one-thirtieth of a wavelength. The impedance of the dipole is therefore predominantly capacitative and is, moreover, comparatively high, although the resistive component of the;

dipole impedance is exceptionally ,low. For an antenna of one-tenth wave-length overall dimensions (i. e. where L is somewhat lowerthan 0.05 7\) for short waves of the order of 15 to 30 meters, the effective resistance component of the dipole is approximately 2 ohms, most of this effective resistance being constituted by the radiation resistance of the dipole. The reactive component of the dipole impedance, however, is very much higher, being of the same order as the capacitative reactance of a section of openended transmission line L units in length.

In order to tune the dipole to resonance by neutralizing the capacitative reactance without introducing further resistive components of comparable magnitude to the radiation resistance, the necessary loading inductance. is provided by that section of transmission line 3 which extends between the dipole and the short circuiting bar 4. The length H of this section of transmission line is adiusted by moving short circuiting bar 4 so that for the frequency to be received,

or radiated, this short circuited section of trans- 1 mission line as modified by certain further equipment connected thereto will present an inductive reactance equal to the capacitative reactance of the dipole'antenna. Since the capacitative reactance of the dipole is roughly the same as the capacitative reactance of an open-ended section of transmission line of length L, the length H of the short 'circuited loop of transmission line will be roughly one-quarter A minus L if the effect of the further equipment associated with this loop is small.

A receiver 1 is connected to one end of transmission line 5, and theother end of this line is adjustably clamped to a suitable point along the resonating section of transmission line '3, the point at which transmission line 5 is clampedto transmission line 3 beingadjusted so as to approximately match the impedances at this point of junction. If the receiver impedance as viewed 'the receiver as well as being matched at its junction with transmission line 3, but ordinarily the arrangement shown is'adequate without further matching means.

A variable condenser 6 of small capacityis connected across. transmission line 3, either at a small distance from the dipole or directly across the dipole antenna. In order to preserve symmetry it is preferred to make condenser E of the split statortype havingtwo insulated stators'and a common rotor; this is particularly desirable when the condenser is connected directly across the dipole. When thecondenser is connected cuiting bar 4. Since the movement of short cir-' cuiting bar 4 varies the matching conditions of movement of the short circuiting pole antenna across the transmission line 3, it is preferred that this condenser should be bridged across this transmission line at a point suiiiciently close to the dipole antenna so as not to interfere with the adjustment of the connecting clamps of trans- 5 mission line 5.

In case a slightly higher efficiency is desirable even at the expense of sacrificing convenience, the, condenser 6 may be omitted and the tuning per-formed solely by adjustment of the short cir- 1o transmission line 5 to a considerable extent, it

will ordinarily be necessary to readjust the point of clamping of transmission line 5 whenever the 15 short circuiting bar 4 is moved by any considerable amount. If the condenser 6 is provided, however, a considerable adjustment of the frequency may be made by varying this condenser without greatly upsetting the matching adjust 20 ment of transmission line 5. Therefore, it is ordinarily preferred to provide the condenser as mentioned, and in this case the short circuiting bar A is only readjusted when changing from one frequency range to another frequency range, whereas small changes between different frequencies in the same'frequenoy range are effectedby adjustment of condenser 5 without necessitating bar 4 of the transmission line 5. g

An antenna of the type described and illustrated in Fig. 1 is particularly useful for portable sending or receiving systems operating on wavelengths between 15 and 30 meters, since for this commercial range of wavelengths the dipole antenna of the usual type is so unwieldy as to be impracticable for portable use, whereas a disystem constructed in accordance with the present invention is sufficiently small to be readily portable. For a wavelength of 20-(4 meters, for example, the dipole antenna of my invention may have an overall length of about six feet or less, while still presenting anefiiciency which is only about one and one-third decibels below the. theoretical maximum. Since there iseg some loss even in the case of an antenna several wavelengths long, it is clear that the reduction in efliciency of my antenna system byvirtue of its very great reduction in length is for all practical purposes negligible.

A receiving system. constructed in accordance I with my invention and having an overall antenna length of less than 0.1 wavelength, has an average radiation efficiency in all directions which in spite of its minute size is substantially as greatztg as that of the largest, most efficient system which could be theoretically imagined. This means that except for possible gains in efficiency in one direction which may be obtained in certain sys terms by corresponding reduction of efficiency 111(3 other directions, the small antenna of my invention will deliver to its receiver about as much power as any possible system regardless of size. .In fact, the power delivered to the receiver by a system. according to my invention is less than2t two decibels below the theoretical maximum.

' Similarly if my invention is used for a transmitting system the power radiated into the ether for a given number of watts supplied from the transmitter will be substantially as great as the jo' I the infficient probe antennae or exploring 'ic previously explainedr 7 2,177,416 3 rods previously used for laboratory and field tennae may be mounted on poles carried in the tests, but is rather to be compared with the much hand or on a motor vehicle, for making observalarger antennae having lengths of one-quarter A, tion of field strength and other field observaone-half and more, which have hitherto been used in all cases where an efiicient radiation or collection of energy was required.

In accordance with a further feature of my invention, a very compact and readily portable direction finding system is provided as shown in Fig. 2. Referring more particularly to this figure, in which similar reference characters represent the same elements as in Fig. 1, the transmission line 3 and short circuiting bar, as well as the transmission line 5 and receiver 7, may be exactly the same as in Fig. 1. Instead of a single dipole Consisting of two conductors l and 2, as in Fig. 1, the direction finding system of Fig. 2 comprises two dipoles parallel to one another and preferably vertically disposed as shown. One of these dipoles consists of the'two conductors la and 2a connected to the transmission line 3 by the branch line 3a. The other dipole is exactly similar, consisting of two conductors lb and 2?) connected to the transmission line 3 by the branch line 3b. In accordance with my invention, not only is the length of each of these dipoles a very small fraction of a wavelength, but also the separation between the two dipoles is made a very small fraction of a wavelength. As shown in Fig. 2, the overall length of each dipole may, for example, be one-tenth A, and the separation between the dipoles may also be one-tenth A. Even smaller dimensions may be used without excessive reduction in efiiciency.

It is preferred, in practising my invention, to maintain the length L of each half-dipole between 0.061 and 0.03)\ in both the system of Fig. 1 andthat of Fig. 2, for most applications of the invention, where the wavelengths used lie within the ordinary commercial band. In the direction finding system of Fig. 2, the condenser 6 may be omitted just as in the system of Fig. 1, although it is preferred to provide this condenser for convenience in making small tuning changes between frequencies of the same general value as The system of Fig. 2 may be used either as a direction finder or as a directional transmitter. Similarly the system of Fig. 1 may be used either as a receiver or a transmitter. When the systems are used as transmitters, it is merely necessary to replace the receivers l by transmitters of corresponding impedance and frequency, and to construct the antenna and transmission line components with sufiiciently strong insulation to withstand a higher voltage.

Both the system of Fig. 1 and the system of Fig. 2 are sufficiently compact so that the antions.

Although certain embodiments of my invention have been described for the purposes of illustration, it will be understood that modifications, adaptations and variations thereof occurring to one skilled in the art, may be made within the scope of my invention as defined by the appended claims.

What I claim is:

1. A short wave antenna system of small dimensions which comprises a dipole antenna having an overall length of the order of one-tenth of the wavelength to be employed, a low loss circult of the transmission line type directly connected to said dipole antenna the combination thereof being resonant at said wavelength, and a wave translating apparatus coupled to said low loss line.

2. A directive short wave antenna system comprising a dipole antenna whose overall length is of the order of one-tenth of the wavelength to be employed, a second similar dipole antenna disposed parallel to said first antenna and spaced therefrom by a distance of the order of onetenth of the wavelength to be employed, a low loss reactive circuit comprising a transmission line connected to tune said two dipole antennae to resonance at the said wavelength, said line being differentially connected to said two dipole antennae so as to neutralize radiant action in a direction perpendicular to the common plane of said two dipole antennae, and means for coupling a wave translating device to a point on said transmission line.

3. A system according to claim 1, further comprising means for adjusting the effective length of said transmission line for tuning the system to difierent frequency ranges, and a variable condenser connected across said line adjacent the connection to said dipole for tuning the system to different frequencies in the same general frequency range.

4. A system for radiant action at wavelengths of the order of 15 to 30 meters, which comprises two antenna conductors each having a length between 0.06 and 0.03), a low loss tuning transmission line connected at one end to said two conductors and effectively short circuited at an adjustable intermediate point to form a resonant circuit with said two conductors, a wave translating device, a second transmission line, means for coupling said device to said second line, and means for coupling said second line to said tuning line in impedance matched fashion.

ANDREW ALFORD. 

